//Sat Jun 19 10:53:42 CDT 2010
#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <queue>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <ctime>

using namespace std;

class EqualizeStrings
{
public:
	string getEq(string s, string t)
	{
		int N= s.size();
		string ret = "";
		for(int i=0; i<N; i++)
		{
			int num = abs(s[i]-t[i]);
			if(num < 13)
				ret += min(s[i],t[i]) + ceil(num/2);
			else
				ret += 'a';
		}
		return ret;
	}
};
